Heat pump type cooling systems have long been known to be reversible to provide both heating and cooling modes. This type of system has an indoor heat exchanger and an outdoor heat exchanger. In the heating mode, the outdoor heat exchanger removes heat from the outdoor air and the indoor heat exchanger acts to transfer this heat to the air in the conditioned space. In the cooling mode, the system is reversed by a reversing valve so that the indoor heat exchanger removes heat from the air in the conditioned space and the outdoor heat exchanger acts to transfer this heat to the outdoor air.
One type of reversing valve presently in use in reversible heat pump type cooling systems consists of an electrically energized solenoid valve which normally opens and/or closes a pilot port to cause a pressure differential across a piston type valve which in turn, causes a slide valve to shift position and reverse the coolant flow in the system. This type of reversing valve reverses refrigerant flow almost instantaneously, and causes substantial reversal shock on the entire system.
The present day reversing valve designs suffer from a number of drawbacks which have been tolerated but which have universally plagued manufacturers of reversible heat pump systems for years. First, the substantial reversal shock caused by the almost instantaneous reversal of refrigerant has caused leakage problems and has necessitated the use of brazed tubing connections. Second, with the present valve designs, foreign material in the refrigerant has caused clogging problems and increased wear on the valve components. This problem can be solved by placing a filter in the system but the filter provides an additional pressure drop which cannot be tolerated in some systems. A third problem area with present designs lies in the use of plastic components in the valve and the present day methods employed in factory and field installation of these valves. In present installation methods, the valve body is connected to system tubing by brazing. Because of the temperatures encountered in the brazing process it is necessary to provide some means to dissipate the heat in order to prevent damage of the plastic valve components. In the prior art reversing valves, the valve is held in the operated position by an electrically energized operator. Thus, prior art reversing valves tend to consume a substantial amount of power. Another problem noted with present reversing valve designs is the requirement of system differential pressures in order to reverse the valve. Thus, with prior art designs, if this pressure differential is not present, the valve cannot operate.